Dynamic stabilization assembly having pre-compressed spacers with differential displacements

ABSTRACT

A dynamic longitudinal connecting member assembly includes an anchor member having an integral or otherwise fixed elongate core extending through at least two elastic spacers and at least one outer sleeve or trolley. The anchor member and the outer sleeve each attach to at least one bone anchor. The spacers have differing durometers and/or geometries, resulting in greater axial movement of the sleeve in one direction than in an opposite direction. The spacers are compressed prior to attachment to the bone anchors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/459,492, filed Jul. 1, 2009 which claimed the benefit of U.S.Provisional Patent Application Ser. No. 61/134,480, filed Jul. 10, 2008and claimed the benefit of U.S. Provisional Patent Application Ser. No.61/137,743, filed Aug. 1, 2008, all of which are incorporated byreference herein. U.S. application Ser. No. 12/459,492 is also acontinuation-in-part of U.S. patent application Ser. No. 12/148,465,filed Apr. 18, 2008, that claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/927,111, filed May 1, 2007, all of which areincorporated by reference herein. Application Ser. No. 12/459,492 isalso a continuation-in-part of U.S. patent application Ser. No.12/156,260, filed May 30, 2008, now U.S. Pat. No. 7,951,170, issued May31, 2011, that claimed the benefit of U.S. Provisional PatentApplication Ser. No. 60/932,567, filed May 31, 2007, and the benefit ofU.S. Provisional Patent Application Ser. No. 60/994,068, filed Sep. 17,2007, all of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention is directed to dynamic fixation assemblies for usein bone surgery, particularly spinal surgery, and in particular tolongitudinal connecting members and cooperating bone anchors orfasteners for such assemblies, the connecting members being attached toat least two bone anchors.

Historically, it has been common to fuse adjacent vertebrae that areplaced in fixed relation by the installation therealong of bone screwsor other bone anchors and cooperating longitudinal connecting members orother elongate members. Fusion results in the permanent immobilizationof one or more of the intervertebral joints. Because the anchoring ofbone screws, hooks and other types of anchors directly to a vertebra canresult in significant forces being placed on the vertebra, and suchforces may ultimately result in the loosening of the bone screw or otheranchor from the vertebra, fusion allows for the growth and developmentof a bone counterpart to the longitudinal connecting member that canmaintain the spine in the desired position even if the implantsultimately fail or are removed. Because fusion has been a desiredcomponent of spinal stabilization procedures, longitudinal connectingmembers have been designed that are of a material, size and shape tolargely resist bending (flexion, extension and lateral), torsion, shear,distraction and compression, and thus substantially immobilize theportion of the spine that is to be fused. Thus, longitudinal connectingmembers are typically uniform along an entire length thereof, andusually made from a single or integral piece of material having auniform diameter or width of a size to provide substantially inelasticrigid support in all planes.

An alternative to fusion, which immobilizes at least a portion of thespine, and the use of more rigid longitudinal connecting members orother rigid structure has been a “soft” or “dynamic” stabilizationapproach in which a flexible loop-, S-, C- or U-shaped member or acoil-like and/or a spring-like member is utilized as an elasticlongitudinal connecting member fixed between a pair of pedicle screws inan attempt to create, as much as possible, a normal loading patternbetween the vertebrae in flexion, extension, side bending, distraction,compression and torsion. Another type of soft or dynamic system known inthe art includes bone anchors connected by flexible cords or strands,typically made from a plastic material. Such a cord or strand may bethreaded through cannulated spacers that are disposed between adjacentbone anchors when such a cord or strand is implanted, tensioned andattached to the bone anchors. The spacers typically span the distancebetween bone anchors, providing limits on the bending, movement of thecord or strand and thus strengthening and supporting the overall system.Shear forces are not well resisted by the typical cord and spacerstabilization systems. Such tensioned cord and spacer systems may alsocause facet joint compression during spinal movement, especiallyflexion.

The complex dynamic conditions associated with spinal movement createchallenges for the design of elongate elastic longitudinal connectingmembers that exhibit an adequate fatigue strength to providestabilization and protected motion of the spine, without fusion, andthat allow for some natural movement of the portion of the spine beingreinforced and supported by the elongate elastic or flexible connectingmember. A further challenge are situations in which a portion or lengthof the spine requires a more rigid stabilization, possibly includingfusion, while another portion or length may be better supported by amore dynamic system that allows for protective movement.

SUMMARY OF THE INVENTION

A longitudinal connecting member assembly according to the invention hasan inner elongate core of circular or non-circular cross-section that isintegral or otherwise fixed to a first bone anchor attachment portion. Afirst elastic spacer surrounds the core and is slidable along the coreat a location between a pair of adjacent bone anchors. At least oneouter inelastic sleeve or tube-like trolley member also surrounds thecore and is in sliding relationship with the core. The outer sleeve alsoengages at least one bone anchor. A second elastic spacer of durometeror geometry differing from the first elastic spacer also surrounds thecore and is located at a side of the at least one sleeve member oppositethe first elastic spacer. The inner core, elastic spacers and inelasticsleeve or sleeves cooperate dynamically, with the spacers being at leastsomewhat pre-compressed resulting in little-to-no or more substantialdeformation of the spacers prior to insertion, and controlling movementof the sleeve allowing greater travel of the sleeve along the core in asingle direction; for example, advantageously allowing greater operativetravel of the sleeve in a cephalad or cranial direction and more limitedmovement in a caudal or caudad direction after insertion. In addition,in certain embodiments, the sleeve or tube trolley members feature innersurfaces having non-linear relief for improved core member function withrespect to bending stress, wear and fatigue life concerns.

In another embodiment, an improved longitudinal connecting memberadapted for cooperating with a plurality of bone anchors that areimplanted in a patient's spine is provided, wherein the longitudinalconnecting member includes a substantially rigid anchor portion thatextends along a longitudinal axis of the connecting member and is joinedwith a core portion that also extends along the longitudinal axis. Theanchor portion formed of a first material and the core portion is formedof a second material. The core portion includes a reduced diameterrelative to the anchor portion, such that the second material and thereduced diameter cooperate so as to enable at least some flexing of thecore portion. The anchor portion is directly engaged by first and secondbone anchors while the core portion is indirectly engaged by a thirdbone anchor. Furthermore, the longitudinal connection member providesfor greater movement in the cephalad direction than in the caudaddirection.

A first inelastic sleeve is slidingly received over the core portion soas to be located between the third bone anchor and the core portion. Apair of elastic spacers is received over the core portion such that eachof the spacers is adjacent to an end of the first sleeve. A crimp ringengages the core portion and is located so as to bias the spacers.Additionally, an elastic over-mold surrounds at least one of the spacersand a respective adjacent end of the first sleeve.

In a further embodiment, the elastic over-mold grips both the anchorportion and the first sleeve.

In another further embodiment, the anchor portion includes has a firstend plate and the elastic over-mold is molded about the first end plate.

In some further embodiments, the elastic over-mold is made from acomposite material comprising elongate reinforcement strands imbedded ina polymer.

In some further embodiments, the core is made from a polymer.Furthermore, in some embodiments, the polymer is polyetheretherketone.

In another further embodiment, the first sleeve substantially blocksflexing of the portion of the core that is surrounded by the firstsleeve. Additionally, in some embodiments, the core flexes primarilybetween the first sleeve and the anchor portion.

In yet another further embodiment, the longitudinal connecting memberalso includes a second inelastic sleeve slidingly received over the coreportion so as to be located between a fourth bone anchor and the coreportion; a third elastic spacer received over the core portion so as tobe located between the second inelastic sleeve and the crip ring; and asecond elastic over-mold surrounding a second end of the first sleeve,the third spacer and an adjacent end of the second sleeve. In someembodiments, the first sleeve substantially blocks flexing of theportion of the core that is surrounded by the first sleeve; and thesecond sleeve substantially blocks flexing of the portion of the corethat is surrounded by the second sleeve. Accordingly, in someembodiments, the core flexes primarily between the first sleeve and theanchor portion; and between the first sleeve and the second sleeve.

Objects and Advantages of the Invention

An object of the invention is to provide dynamic medical implantstabilization assemblies having longitudinal connecting members thatinclude a flexible, pre-tensioned portion that can allow for controlledbending, torsion, compression and distraction of the assembly. Anotherobject of the invention is to provide such an assembly including elasticpre-compressed spacers of various durometers and/or geometries. Afurther object of the invention is to provide dynamic medical implantlongitudinal connecting members that may be utilized with a variety ofbone screws, hooks and other bone anchors. Additionally, it is an objectof the invention to provide a lightweight, reduced volume, low profileassembly including at least two bone anchors and a longitudinalconnecting member therebetween. Furthermore, it is an object of theinvention to provide apparatus and methods that are easy to use andespecially adapted for the intended use thereof and wherein theapparatus are comparatively inexpensive to make and suitable for use.

Other objects and advantages of this invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention.

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention and illustrate variousobjects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged side elevational view of a dynamic fixationconnecting member assembly according to the invention.

FIG. 2 is a reduced side elevational view of the assembly of FIG. 1shown with four bone screws and in an operative position with respect toa human spine.

FIG. 3 is an enlarged and partial exploded perspective view of theassembly of FIG. 1 including a solid core anchor, a first differentialcompression spacer, a first pressure washer, a first sleeve, a secondpressure washer, a second differential compression spacer, a thirdpressure washer, a second sleeve, an elastic bumper and a crimping ring.

FIG. 4 is an enlarged and partial cross-sectional view taken along theline 4-4 of FIG. 1 and with two optional over-molded coverings shown inphantom.

FIG. 5 is an enlarged side elevational view of the solid core anchor ofFIG. 3.

FIG. 6 is an enlarged top plan view of the first differentialcompression spacer of FIG. 3.

FIG. 7 is an enlarged bottom plan view of the first spacer of FIG. 3.

FIG. 8 is an enlarged side elevational view of the first spacer of FIG.3.

FIG. 9 is an enlarged cross-sectional view taken along the line 9-9 ofFIG. 6.

FIG. 10 is an enlarged top plan view of the first pressure washer ofFIG. 3.

FIG. 11 is an enlarged side elevational view of the first pressurewasher of FIG. 3.

FIG. 12 is an enlarged cross-sectional view taken along the line 12-12of FIG. 10.

FIG. 13 is an enlarged side elevational view of the first sleeve of FIG.3.

FIG. 14 is an enlarged top plan view of the first sleeve of FIG. 3.

FIG. 15 is an enlarged cross-sectional view taken along the line 15-15of FIG. 14.

FIG. 16 is an enlarged top plan view of the second spacer of FIG. 3.

FIG. 17 is an enlarged side elevational view of the second spacer ofFIG. 3.

FIG. 18 is an enlarged cross-sectional view taken along the line 18-18of FIG. 16.

FIG. 19 is, an enlarged top plan view of the second sleeve of FIG. 3.

FIG. 20 is an enlarged bottom plan view of the second sleeve of FIG. 3.

FIG. 21 is an enlarged side elevational view of the second sleeve ofFIG. 3.

FIG. 22 is an enlarged cross-sectional view taken along the line 22-22of FIG. 19.

FIG. 23 is an enlarged top plan view of the bumper of FIG. 3.

FIG. 24 is an enlarged side elevational view of the bumper of FIG. 3.

FIG. 25 is an enlarged cross-sectional view taken along the line 25-25of FIG. 23.

FIG. 26 is an enlarged top plan view of the crimping ring of FIG. 3.

FIG. 27 is an enlarged side elevational view of the crimping ring ofFIG. 3.

FIG. 28 is an enlarged cross-sectional view taken along the line 28-28of FIG. 26.

FIG. 29 is an enlarged exploded perspective view of a portion of one ofthe bone screws shown in FIG. 2.

FIG. 30 is an enlarged perspective view of the connecting member of FIG.1 shown with one of the bone screws of FIG. 2 in exploded perspectiveview.

FIG. 31 is an enlarged and partial side elevational view of the assemblyof FIG. 1, shown with a bone screw of FIG. 2, with portions broken awayto show the detail thereof.

FIG. 32 is a partial side elevational view of the assembly of FIGS. 1and 2 with optional over-molds shown in phantom and with differentialdisplacement in a caudal direction.

FIG. 33 is a partial side elevational view of the assembly of FIGS. 1and 2 with optional over-molds shown in phantom and with differentialdisplacement in a cephalad direction.

FIG. 34 is a side elevational view of the assembly of FIGS. 1 and 2 withoptional over-molds shown in phantom and shown operatively responding tospinal extension or lordosis.

FIG. 35 is an enlarged and partial side elevational view, similar toFIG. 34 with portions broken away to show the detail thereof.

FIG. 36 is a rear elevational view of the assembly of FIGS. 1 and 2 withoptional over-molds shown in phantom and shown operatively responding tospinal scoliosis.

FIG. 37 is an enlarged and partial rear elevational view, similar toFIG. 36 with portions broken away to show the detail thereof.

FIG. 38 is an enlarged side elevational view of a second embodiment of adynamic connecting member assembly according to the invention shown withthree bone screws.

FIG. 39 is an enlarged and exploded side elevational view of theassembly of FIG. 38.

FIG. 40 is an enlarged side elevational view of the assembly of FIG. 38with the optional over-mold in phantom.

FIG. 41 is an enlarged and partial side elevational view of the assemblyof FIG. 38 with the optional over-mold shown in phantom and the spacershown under operative compression.

FIG. 42 is a partial side elevational view of the assembly of FIG. 38with the optional over-mold shown in phantom and differentialdisplacement in a cephalad direction in response to spinal distractionor tension.

FIG. 43 is a side elevational view of the assembly of FIG. 38 with theoptional over-mold shown in phantom and shown in compression andoperatively responding to spinal extension or lordosis.

FIG. 44 is an enlarged side elevational view of the assembly of FIG. 38with the optional over-mold shown in phantom and shown operativelyresponding to spinal distraction as well as flexion.

FIG. 45 is an enlarged side elevational view of a third embodiment of adynamic connecting member assembly according to the invention.

FIG. 46 is a reduced and partial exploded perspective view of theassembly of FIG. 45.

FIG. 47 is an enlarged and partial cross sectional view taken along theline 47-47 of FIG. 45 with an optional over-mold shown in phantom.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure. It is also noted that any reference tothe words top, bottom, up and down, and the like, in this applicationrefers to the alignment shown in the various drawings, as well as thenormal connotations applied to such devices, and is not intended torestrict positioning of the connecting member assemblies of theapplication and cooperating bone anchors in actual use.

With reference to FIGS. 1-37, the reference numeral 1 generallydesignates a non-fusion dynamic stabilization longitudinal connectingmember assembly according to the present invention. The connectingmember assembly 1 includes an inelastic anchor member, generally 4,having an inelastic elongate inner core 6 extending from a bone anchorattachment portion 8; a first elastic differential compression spacer10; a first hard or inelastic contoured pressure washer 11; a firstinelastic sleeve or sleeve trolley 12; a second inelastic contouredpressure washer 13; a second elastic differential compression spacer 14;a third inelastic contoured pressure washer 15; a second inelasticsleeve 16; a third elastic differential compression spacer or elasticbumper 18; and an inelastic crimping ring 20; all substantiallysymmetrically aligned with respect to a central axis A of the anchormember 4. The elongate core 6 of the anchor member 4 is receivablewithin the spacers, sleeves, pressure washers, bumper and crimping ring.Thus, the axis A of the anchor member 4 is also the axis of the fullyassembled assembly 1. An optional over-molded sleeve or casing 22 cansurround a portion of the anchor member 4 extending to the bone anchorattaching portion 8, the spacer 10, the washer 11 and a portion of thesleeve 12. A second over-molded sleeve or casing 23 surrounds a portionof the sleeve 12, the washer 13, the spacer 14, the washer 15 and aportion of the sleeve 16. As will be described in greater detail below,when fully assembled and all components fixed in position, as shown inFIGS. 1, 2 and 4, for example, the spacers 10 and 14 and the bumper 18are in compression, with the more elastic bumper 18 shown being slightlydeformed and bulging outwardly due to the compressive force placedthereupon. The pre-compressed spacers and bumpers in turn place axialforces upon the sleeves 12 and 16, the sleeves thus being in a dynamicrelationship with the spacers and movable with respect to the core. Inparticular, FIG. 2 illustrates placement of the assembly 1 andcooperating bone screws as positioned along a human spine with theelastic bumper 18 being at a top or upper position, the bumper 18 andspacers 10 and 14 having varying elasticities to allow for more movementof the assembly 1 in a cephalad or cranial direction and more limitedmovement in a caudad direction.

As illustrated in FIG. 2, the dynamic connecting member assembly 1cooperates with at least three bone anchors and is illustrated with fourbone anchors in the form of polyaxial bone screws, generally 25, theassembly 1 being captured and fixed in place at the anchor portion 8,the inelastic sleeve 12 and the inelastic sleeve 16 by the bone screws25. Because the anchor portion 8 and the sleeves 12 and 16 havesubstantially solid, substantially hard, inelastic cylindrical surfaces,the connecting member assembly 1 may be used with a wide variety of bonescrews and other bone anchors already available for cooperation withmore rigid rods including fixed, monoaxial bone screws, hinged bonescrews, polyaxial bone screws, and bone hooks and the like, with orwithout compression inserts, that may in turn cooperate with a varietyof closure structures having threads, flanges, or other structure forfixing the closure structure to the bone anchor, and may include otherfeatures, for example, external or internal drives, break-off tops andinner set screws. The bone anchors, closure structures and theconnecting member assembly 1 are then operably incorporated in anoverall spinal implant system for correcting degenerative conditions,deformities, injuries, or defects to the spinal column of a patient.

In the particular embodiment of the assembly 1 being illustrated herein,wherein the sleeves 12 and 16 are advantageously relatively thin so asto result in an assembly having a low profile, the bone screws 25 areequipped with upper and lower pressure inserts to closely hold thesleeves and yet not crush the sleeves against the inner core 6. Inparticular, with reference to FIGS. 29, 30 and 31, the illustratedpolyaxial screws 25 each include a shank 27, a receiver or head 28, alower pressure insert 29, an upper pressure insert 30 and a closurestructure, generally 32 that further includes and outer fastener 33 andan inner set screw 34. The illustrated shank 27 for insertion into avertebra (not shown) is pivotally attached to the open receiver or head28. The shank 27 includes a threaded outer surface and optionallyincludes a central cannula or through-bore disposed along an axis ofrotation of the shank 27. The through bore provides a passage throughthe shank interior for a length of wire or pin inserted into thevertebra prior to the insertion of the shank 27, the wire or pinproviding a guide for insertion of the shank 27 into the vertebra. Thereceiver 28 includes a pair of spaced and generally parallel arms thatform an open generally U-shaped channel therebetween that is open atdistal ends of such arms. The receiver arms each include radially inwardor interior surfaces that have a discontinuous guide and advancementstructure mateable with cooperating structure on the outer fastener 33.The guide and advancement structure may be a partial helically woundflangeform configured to mate under rotation with a similar structure onthe outer fastener 33 or a buttress thread, a square thread, a reverseangle thread or other thread like or non-thread like helically woundadvancement structures for operably guiding under rotation and advancingthe fastener 33 downward between the receiver arms and having such anature as to resist splaying of the receiver arms when the fastener 33is advanced between the receiver arms.

The illustrated shank 27 is top loaded into the receiver 28 and has acurved head for sliding, pivotal engagement with an inner surface of thereceiver 28. However, a variety of polyaxial connections may bepossible. For example, a spline capture connection as described in U.S.Pat. No. 6,716,214, and incorporated by reference herein, may be usedwherein the bone screw shank includes a capture structure mateable witha retaining structure disposed within the receiver. The retainingstructure includes a partially spherical surface that is slidinglymateable with a cooperating inner surface of the receiver, allowing fora wide range of pivotal movement between the shank 27 and the receiver28. Polyaxial bone screws with other types of capture connections mayalso be used according to the invention, including but not limited to,threaded connections, frictional connections utilizing frusto-conical orpolyhedral capture structures, integral top or downloadable shanks, andthe like. Also, as indicated above, polyaxial and other bone screws foruse with connecting members of the invention may have bone screw shanksthat attach directly to the connecting member or may include compressionmembers or inserts, such as the members 29 and 30 that engage the bonescrew shank and cooperate with the shank, the receiver and the closurestructure to secure the connecting member assembly to the bone screwand/or fix the bone screw shank at a desired angle with respect to thebone screw receiver that holds the longitudinal connecting memberassembly. Furthermore, although the closure structure 32 of the presentinvention is illustrated with the polyaxial bone screw 25 having an openreceiver or head 28, it foreseen that a variety of closure structuresmay be used in conjunction with any type of medical implant having anopen or closed head or receiver, including monoaxial bone screws, hingedbone screws, hooks and the like used in spinal surgery.

To provide a biologically active interface with the bone, the threadedshank 27 may be coated, perforated, made porous or otherwise treated.The treatment may include, but is not limited to a plasma spray coatingor other type of coating of a metal or, for example, a calciumphosphate; or a roughening, perforation or indentation in the shanksurface, such as by sputtering, sand blasting or acid etching, thatallows for bony ingrowth or ongrowth. Certain metal coatings act as ascaffold for bone ingrowth. Bio-ceramic calcium phosphate coatingsinclude, but are not limited to: alpha-tri-calcium phosphate andbeta-tri-calcium phosphate (Ca₃(PO₄)₂, tetra-calcium phosphate(Ca₄P₂O₉), amorphous calcium phosphate and hydroxyapatite(Ca₁₀(PO₄)₆(OH)₂). Coating with hydroxyapatite, for example, isdesirable as hydroxyapatite is chemically similar to bone with respectto mineral content and has been identified as being bioactive and thusnot only supportive of bone ingrowth, but actively taking part in bonebonding. It is also foreseen that combinations of the above can be used,such as a composite of titanium plasma spray and hydroxyapatite.

The closure structure 32 can be any of a variety of different types ofclosure structures for use in conjunction with the present inventionwith suitable mating structure on the interior surface of the upstandingarms of the receiver 28. The illustrated closure structure 27 is in twopieces with the outer fastener 33 rotatable between the spaced arms andthe inner set screw 34 rotatable within the outer fastener 33. However,single piece closures may be used and other structures, such as slide-inclosure structures may be used as an alternative to helically woundclosures. The illustrated outer fastener 33 is substantially cylindricaland includes an outer helically wound guide and advancement structure inthe form of a flange form that may take a variety of forms, includingthose described in Applicant's U.S. Pat. No. 6,726,689, which isincorporated herein by reference. It is also foreseen that according tothe invention the closure structure guide and advancement structurecould alternatively be a buttress thread, a square thread, a reverseangle thread or other thread like or non-thread like helically woundadvancement structure for operably guiding under rotation and advancingthe closure structure downward between the receiver arms and having sucha nature as to resist splaying of the arms when the closure structure isadvanced into the U-shaped channel formed by the arms. The illustratedclosure 32 further includes the inner set screw 34 with an internaldrive in the form of an aperture utilized for assembly of the set screwand removal of the entire closure 32. It is foreseen that the closurestructure may alternatively include an external drive, such as abreak-off head designed to allow such a head to break from a base of theclosure at a preselected torque, for example, 60 to 120 inch pounds.Such a closure structure would also include a base having an internaldrive to be used for closure removal.

Returning to the longitudinal connecting member assembly 1 illustratedin FIGS. 1-37, the assembly 1 is elongate, with the inner core 6 being asubstantially solid, smooth and in the form of a uniform cylinder or rodhaving an outer cylindrical surface 36 and a substantially circularcross-section. The core 6 and integral anchor attachment portion 8 maybe made from metal, metal alloys or other suitable materials, includingplastic polymers such as polyetheretherketone (PEEK),ultra-high-molecular weight-polyethylene (UHMWP), polyurethanes andcomposites, including composites containing carbon fiber and layers ofdifferent materials. It is noted that although an anchor member 4 isillustrated in which the components 6 and 8 are integral, the core 6 andthe anchor attachment portion 8 may be made from different materials,for example, the core 6 may be made out of PEEK and inserted into andfixed and/or adhered to a bone anchor attachment portion 8 made out oftitanium. The core 6 and attachment portion 8 may include a smallcentral lumen or through-bore (not shown) extending along the centralaxis A. Such a lumen may be used as a passage through the entireassembly 1 interior for a length of a guide wire for aiding insertion ofthe assembly 1 between implanted bone screws 25 in a percutaneous orless invasive procedure.

With particular reference to FIGS. 3 and 5, the anchor member 4 issubstantially cylindrical along an entire length thereof along the axisA and includes at least two or more circular cross-sections along thelength thereof. The illustrated member 4 includes the slender and thusmore flexible core 6 of a first circular cross-section and the boneanchor attachment portion 8 that has a second circular cross-sectionthat is larger than the core 6 cross-section and thus is more rigid thanthe core 6. The core 6 terminates at an end 38. Prior to final assemblyby the vendor or manufacturer, the core 6 is typically of a lengthgreater than that shown in the drawing figures so that the core 6 may begrasped by a tool (not shown) near the end 38 and pulled along the axisA in a direction away from the anchor attachment portion 8, in certainembodiments, tensioning the core 6 and putting compressive forces on thespacers and bumper, as will be described in greater detail below.Between the core 6 and the portion 8 is a buttress plate or annularenlargement 40 that has a third circular cross-section that is largerthan the attachment portion 8 cross-section. The buttress plate 40 isintegral with and disposed between the core 6 and the portion 8.Although the illustrated anchor member 4 is substantially cylindrical,it is foreseen that the core 6, the portion 8 and the plate 40 may haveother forms, including but not limited to oval, square and rectangularcross-sections as well as other curved or polygonal shapes. The boneanchor attachment portion 8 is of a length along the axis A forcooperating with at least one and up to a plurality of bone attachmentmembers, such as the bone screws 25, hooks or other types of boneanchors. The portion 8 is substantially solid and rigid, with an outercylindrical surface 39 that terminates at an end 41. The plate 40includes a first substantially flat and annular face 42 facing away fromthe core 6 and an opposed face 44 facing toward the core 6. The faces 42and 44 extend radially from the axis A. An outer cylindrical surface 46extends between the faces 42 and 44. A gently sloping transition surfaceor flange 48 bridges between and connects the outer cylindrical surface36 of the core 6 with the substantially flat facing face 44 of thebuttress plate 40.

With particular reference to FIGS. 13-15 and 19-22, the sleeves 12 and16 are each sized and shaped to be slidingly received over the core 6along the axis A and each have a length measured along the axis A thatis sufficient for the attachment of at least one bone screw 25 thereon.Similar to the inelastic anchor member 4, the inelastic sleeves 12 and16 may be made from metal, metal alloys or other suitable materials,including plastic polymers such as polyetheretherketone (PEEK),ultra-high-molecular weight-polyethylene (UHMWP), polyurethanes andcomposites, including composites containing carbon fiber. The sleeves 12and 16 may be made of the same material as the cooperating core 6, forexample, the anchor member 4 and the sleeves 12 and 16 may all be madefrom PEEK; or, for example, the core 6 may be made from one material,such as PEEK, while the sleeves 12 and 16 may be made from anothermaterial, such as a metal (e.g. stainless steel or titanium). In orderto have low or no wear debris, the sleeve 12 and 16 inner surfacesand/or cooperating core 6 outer surfaces may be coated with an ultrathin, ultra hard, ultra slick and ultra smooth coating, such as may beobtained from ion bonding techniques and/or other gas or chemicaltreatments.

The illustrated sleeves 12 and 16 each are substantially cylindrical,having outer cylindrical bone anchor attachment surfaces 50 and 52,respectively, that are each of substantially the same diameter as theouter surface 39 of the bone anchor attachment portion 8. Each of thesleeves 12 and 16 further include a substantially cylindrical innersurface 54 and 56, respectively, that define a through-bore for thepassage of the core 6 therethrough. While the surface 56 is shown asbeing cylindrical, the illustrated surface 54 of the sleeve 12 ispreferably curved and shown as slightly hour-glass or hyperboloid-likein configuration running along the axis A, and/or at least hasnon-linear relief at one or both ends. The slightly curved surface 54results in at least a partially non-linear inner lumen that decreasesboth bending stresses along the core 6 and wear debris between theparts. For example, if the core 6 is flexed, the inner surface 54 allowsdeformation of the core over a longer area or length resulting inreduced stresses and a longer fatigue life. Furthermore, if the core 6is made from a material such as PEEK, the curved surface 54 and/or endsurface non-linear relief reduces contact wear and bending stressesalong the core 6 surface that is received in the sleeve 12. The sleeve12 includes a pair of opposed end plates 58 and 60 and the sleeve 16includes a pair of opposed end plates 62 and 63. The illustrated plates58, 60, 62 and 63 have outer cylindrical surfaces 64, 66, 68 and 69,respectively, that are of substantially the same diameter as thebuttress plate outer cylindrical surface 46. The sleeve 12 includesopposed curved and slightly concave flanged end surfaces 70 and 72, eachrunning from the inner surface 54 radially outwardly toward respectivecylindrical surfaces 64 and 66. The illustrated concave surfaces 70 and72 are partially spherical. The sleeve 16 includes one concave endsurface 74 and an opposed planar end surface 76. The illustrated surface74 is partially spherical.

With reference to FIGS. 6-9, 16-18 and 23-25, the elastic spacers 10 and14 and the elastic bumper 18 are sized and shaped to be slidinglyreceived over the core 6 and may be made from a variety of elasticmaterials of different durometers and materials, including, but notlimited to natural or synthetic elastomers such as polyisoprene (naturalrubber), and synthetic polymers, copolymers, and thermoplasticelastomers, for example, polyurethane elastomers such aspolycarbonate-urethane elastomers. In order to have low or no weardebris, the spacers 10 and 14 and bumper 18 inner and side surfaces mayalso be coated with an ultra thin, ultra hard, ultra slick and ultrasmooth coating, such as may be obtained from ion bonding techniquesand/or other gas or chemical treatments.

The illustrated spacers 10 and 14 advantageously cooperate with the core6 of the anchor member 4, providing directed axial movement, limitationand protection of movement by the sleeves 12 and 16 along the core 6located between bone screws 25. With particular reference to FIGS. 6-9and 16-18, the illustrated spacers 10 and 14 are substantially similarin geometry, differing only with regard to inner surfaces that definethrough bores for receiving the anchor member core 6 and number ofoptional outer grooves. Each of the spacers 10 and 14 have an externalsubstantially cylindrical outer surface 78 and 80, respectively, andinternal surfaces 82 and 84, respectively, each defining through bores.The internal surface 82 is further defined by a flared or conicaloutwardly extending surface 86 sized and shaped for cooperating with thetransition surface 48 of the anchor member 4. The spacer 10 includesopposed substantially planar and annular end surfaces 88 and 89 and thespacer 14 includes opposed substantially planar and annular end surfaces90 and 91. When cooperating with the core 6, the end surfaces 88 and 89and 90 and 91 are substantially perpendicular to the axis A. It isforeseen that in some embodiments, the spacers 10 and 14 may be ofcircular, square, rectangular or other cross-section including curved orpolygonal shapes. In the illustrated embodiment, both the spacers 10 and14 further include optional compression grooves, the spacer 10 having asingle groove 93 and the spacer 14 having a pair of grooves 94 and 95.Spacers according to the invention may include one, none or any desirednumber of grooves that allow for some additional compression of thespacers 10 and 14 when pressed upon in an axial direction between thebone anchor attachment portion 8 and the cooperating sleeves 12 and 16.The illustrated groove 93 and groove pair 94 and 95 are substantiallyuniform and circular in cross-section, being formed in the respectiveexternal surfaces 78 and 80 and extending radially toward respectiveinternal surfaces 82 and 84. The size of the internal surfaces 82 and 84allow for some axially directed sliding movement of the respectivespacers 10 and 14 with respect to the core surface 36. The illustratedspacer 14 is more elastic than the spacer 10, both with respect togeometry, by having more grooves than the spacer 10 and also may be madefrom a material with greater elasticity (lower durometer) than thespacer 14, resulting in an assembly that advantageously provides forgreater travel of the assembly in a cephalad direction, if desired.

With particular reference to FIGS. 10-12, the domed articulating wear orpressure washer 11 is shown. With reference to FIG. 3, for example, itis noted that the pressure washers 13 and 15 are identical to theillustrated pressure washer 11, thus the discussion herein of thepressure washer 11 also applies to the washers 13 and 15. The pressurewasher 11 has an external substantially cylindrical outer surface 98 andinternal substantially cylindrical surface 100, defining a through boresized and shaped to receive the core 6. The washer 11 further includes asubstantially planar end surface 102 and an opposed, curved, convexsurface 104 sized and shaped for cooperation with a substantiallyconcave surface of a cooperating sleeve, such as the surface 70, surface72 or the surface 74. The illustrated convex surface 104 is at leastpartially spherical. When cooperating with the core 6, the end surface102 is substantially perpendicular to the axis A. The size of theinternal surface 100 allows for some axially directed sliding movementof the washer 11 with respect to the core surface 36. The washer 11 ispreferably made from a firm material, such as metal and metal alloyswith titanium being particularly preferred; or other suitable materials,including plastic polymers such as polyetheretherketone (PEEK),ultra-high-molecular weight-polyethylene (UHMWP), polyurethanes andcomposites, including composites containing carbon fiber. In order toreduce wear debris, the washers 11, 13 and 15 are preferably made from amaterial different than the cooperating sleeves 12 and 16. For example,the sleeves 12 and 16 may be made of a titanium alloy while the washers11, 13 and 15 may be made from a high molecular weight polyethylene.With particular reference to the washer 11 and as shown in FIG. 4, withthe convex surface 104 slidingly engaging the concave surface 72 of thesleeve 12, the pressure washer 11 advantageously allows for tilt, slideand rotation of the washers along the core 6 and with respect to thesleeve 12, maintaining substantially full contact between the washer 11and the sleeve 12, resulting in better load distribution along theassembly 1, keeping stresses on the inside of the tubular sleeve 12,rather than on an outer surface or end, and thus allowing for betterangulation, translation and compression of the entire assembly 1, aseach of the pressure washers 11, 13 and 15 have curved, convex surfacesfully contacting and cooperating with substantially similarly curvedconcave inner surfaces of the sleeves 12 and 16. Thus, the core 6,cooperating compressible spacers 10 and 14, sleeves 12 and 16 andwashers 11, 13 and 15 allow for some twist or turn, providing somerelief for torsional stresses.

The over-molded coverings 22 and 23 are preferably thin, soft andelastic, primarily provide protection to the body by keeping wear debriswithin the assembly 1 and keeping scar tissue out of the assembly 1 atthe juncture between the spacers, washers and sleeves. Particularly whenthe assembly 1 is placed in tension as shown in FIG. 33, the over-moldedsections 22 and 23 provide a covering over the components that mayseparate, for example, the pressure washer 11 and the sleeve 12,guarding against gaps that might otherwise irritate scar and surroundingbody tissue. The over-molded sections 22 and 23 may be made of a varietyof materials including natural and synthetic plastics and composites.The illustrated over-molds 22 and 23 are a molded thermoplasticelastomer, for example, polyurethane or a polyurethane blend; however,any suitable polymer material may be used.

The illustrated over-mold 22 is fabricated around and about the surfaces42 and 46 of the anchor plate 40, the entire spacer 10, the entirewasher 11 and the entire end plate 60 of the sleeve 12. The illustratedover-mold 23 is fabricated around and about the surfaces of the endplate 58 of the sleeve 12, the entire washer 13, the entire spacer 14,the entire washer 15 and the entire end plate 63 of the sleeve 16. Theover-molds 22 and 23 are fabricated from an initially flowing elastomer,as will be described more fully below, with the elastomer engaging andpossibly adhering to the surfaces of the sleeves, washers and spacersbeing covered thereby. Each formed elastomer is substantiallycylindrical, but thin so as to also be flexible and deformable when theassembly 1 is bent, compressed or stretched as shown in the drawingfigures. In both spinal flexion and extension, the over-molds 22 and 23completely surround or cover the assembly 1 components as alsoillustrated in the drawing figures. It is foreseen that the material forthe over-molds 22 and 23 may be sized and made from such materials so asto provide for relatively more or less bendability, as well ascompressibility and stretchability.

With particular reference to FIGS. 23-25, the elastic bumper 18 issubstantially cylindrical, including an outer surface 108 and an innersurface 109 forming a substantially cylindrical through bore that opensat planar end surfaces 110 and 111 and operatively extends along theaxis A. The bumper 18 may further include a compression groove orgrooves similar in form and function to the compression grooves 93, 94and 95 described above with respect to the spacers 10 and 14. The bumper18 is sized and shaped to slidingly receive the core 6 through the innersurface 109. The bumper 18 is preferably made from an elastomericmaterial such as polyurethane, but may be made from any suitableelastomeric material. The bumper 18 is typically more elastic thaneither of the spacers 10 and 14, providing greater movement of thesleeve 16 in a direction toward the bumper 18 than toward the spacer 14.

With particular reference to FIGS. 26-28, the crimping ring 20 issubstantially cylindrical and includes an outer surface 120 and an innersurface 122 forming a substantially cylindrical through bore that opensat planar end surfaces 124 and 126 and operatively extends along theaxis A. The crimping ring 20 is sized and shaped to receive the elongatecore 6 through the inner surface 122. The crimping ring 20 furtherincludes a pair of opposed crimp or compression grooves 130 that arepressable and deformable inwardly toward the axis A upon pre-compressionof the spacers 10 and 14 and the bumper 18 during assembly of theassembly 1. The crimping ring 20 is preferably made from a stiff, butdeformable material, including metals and metal alloys. As analternative to the grooves 130, in certain embodiments of the invention,the crimp ring 20 may include an inner helical thread (not shown) withthe core 6 having a mating helical outer thread (not shown), for fixingthe ring 20 on the core 6 and compressing the spacers 10 and 14 andbumper 18 to a desired degree.

The illustrated dynamic connecting member assembly 1 havingpre-compressed spacers is shown cooperating with four polyaxial bonescrews 25 as shown in FIG. 2. In use, the bone screws 25 are implantedinto vertebrae (not shown). Each vertebra may be pre-drilled to minimizestressing the bone. Furthermore, when a cannulated bone screw shank isutilized, each vertebra will have a guide wire or pin inserted thereinthat is shaped for the bone screw cannula of the bone screw shank 27 andprovides a guide for the placement and angle of the shank 27 withrespect to the cooperating vertebra. A further tap hole may be made andthe shank 27 is then driven into the vertebra by rotation of a drivingtool (not shown) that engages a driving feature on or near a top portionof the shank 27. It is foreseen that both the screws 25 and thelongitudinal connecting member assembly 1 may be inserted in aconventional, percutaneous or other minimally invasive surgical manner.

With particular reference to FIGS. 1-4, the longitudinal connectingmember assembly 1 is assembled to provide pre-compressed spacers 10 and14 and bumper 18 prior to implanting the assembly 1 in a patient. FIGS.1, 2 and 4 illustrated the pre-compressed, ready to use assembly 1,while FIG. 32 illustrates the assembly 1 during spinal movement thatresults in further compression of the spacers 10 and 14, while FIG. 33illustrates the assembly 1 during spinal movement that results infurther compression of the bumper 18 and extension of the assembly 1 atthe spacers 10 and 14. With particular reference to FIG. 3, the assembly1 is assembled by first providing the anchor member 4 that has a core 6that is longer in the axial direction A than the core 6 illustrated inthe drawing figures. The spacer 10 is first loaded onto the core 6 byinserting the core 6 end 38 into the bore defined by the inner surface82 with the face 89 directed toward the buttress plate 40. The spacer 10is moved along the core 6 until the surface 86 contacts the surface 48.The pressure washer 11 is then threaded on the core 6 with the face 102facing the end surface 88 of the spacer 10. The sleeve 12 is thenthreaded onto the core 6 with the concave face 72 of the plate 60 facingthe convex surface 104 of the pressure washer 11. The core 6 is thenreceived in the bore of the pressure washer 13, with the convex face ofthe washer 13 facing the concave face 70 of the sleeve 12. The spacer 14is thereafter loaded onto the core 6 by inserting the core 6 end 38 intothe bore defined by the inner surface 84 with the face 91 facing thetoward the pressure washer 13. The spacer 14 is moved along the core 6until the spacer 14 contacts the pressure washer 13. The pressure washer15 is then threaded on the core with a planar face thereof facing theplanar face 90 of the spacer 14. The sleeve 16 is then threaded onto thecore 6 with the concave face 74 facing the convex end surface of thepressure washer 15. The core 6 is received in the bore defined by theinner cylindrical surface 56 and the sleeve 16 is moved along the core 6until the sleeve 16 abuts the pressure washer 15. The bumper 18 isthereafter loaded onto the core 6 by inserting the core 6 end 38 intothe bore defined by the inner surface 109 with the face 111 facing thetoward the planar end surface 76 of the sleeve 16. The bumper 18 ismoved along the core 6 until the surface 111 contacts the surface 76.The crimping ring 20 is thereafter loaded onto the core 6 by insertingthe core 6 end 38 into the bore defined by the inner surface 122 withthe face 126 facing the toward the surface 110 of the bumper 18. Thecrimping ring 20 is moved along the core 6 until the surface 126contacts the surface 110. It is noted that due to the symmetrical natureof the sleeve 12, the spacer 14, the bumper 18 and the crimping ring 20,these components may be loaded onto the core 6 from either side thereof.

After the crimping ring 20 is loaded onto the core 6, manipulation tools(not shown) are used to grasp the core 6 near the end 38 and at the boneanchor attachment portion 8, placing some tension on the core 6. Thespacer 10, the sleeve 12, the spacer 14, the sleeve 16, the bumper 18and the crimping ring 20 are moved toward the buttress plate 40 and intocontact with one another. A desired amount of axial compressive force isplaced on the components loaded on the core 6, followed by deforming thecrimping ring at the crimp grooves 120 and against the core 6. When themanipulation tools are released, the crimping ring 20, now firmly andfixedly attached to the core 6 holds the spacers 10 and 14 and thebumper 18 in compression and the spacers and bumper place axial tensionforces on the core 6, resulting in a dynamic relationship between thecore 6 and the spacers 10, 14 and the bumper 18. The spacers 10 and 16are slidable with respect to the core 6, but also are limited by thebuttress plate of the anchor member 4 and end plates of the sleeves 12and 16. Furthermore, the bumper 18 that is compressed between the sleevesurface 76 and the crimping ring surface 116 is also slidable withrespect to the core 6. The spacers 10 and 14 and the bumper 18 place adistractive force on the core 6 along the axis A and between thebuttress plate 40 and the crimping ring 20, but also are movable withrespect to the core 6, thus being able to respond to jolting and otherbody movements and thereafter spring back into an originally setlocation. The sleeves 12 and 16 that may compress slightly, but are morerigid than the spacers 10 and 14, keep the spacers 10 and 14 in anapproximate desired axially spaced relation. However, the spacers 10 and14 also advantageously slide along the core 6 in response to outsideforces. The core 6 is then trimmed to be approximately flush with theend surface 114 of the crimping ring 20.

It is noted that mechanical characteristics of the assembly components,such as creep, may require the spacers 10 and 14 and the bumper 18 to becompressed at a higher load and then allowed to reach a steady statebefore placement and molding of the over-mold coverings 22 and 23 andeventual operative use with the bone screws 25. The over-molds 22 and 23are fabricated by first placing the anchor portion 8 and/or the sleeves12 or 16 in a jig or other holding mechanism such that the jigfrictionally engages such portion 8 and/or sleeves 12 and 16, followedby fabricating the over-mold 22 about and between the plate 40, thespacer 10, the pressure washer 11 and an end portion of the sleeve 12and the over-mold 23 about and between an opposite end portion of thesleeve 12, the washer 13, the spacer 14, the washer 15 and an endportion of the sleeve 16 as best shown in phantom in FIG. 4. In apreferred method of fabrication of the over-molds 22 and 23, an elastic,polymeric material flows about the desired components of the assembly 1at room temperature, followed by a vacuum cure. It is noted that in someembodiments of the invention, the over-molds 22 and 23 may be fabricatedabout the desired assembly 1 components prior to compression of thespacers 10 and 14 and the bumper 18. In other embodiments, theover-molds 22 and 23 may be fabricated about the spacers 10 and 14 afteran initial compression of the spacers, followed by a final compressionstep after cure of the over-molds.

With reference to FIGS. 2 and 29-37, the assembly 1 is eventuallypositioned in an open or percutaneous manner in cooperation with thebone screws 25 with the over-molds 22 and 23 disposed between bonescrews 25, with a bone screw attached to each of the sleeves 12 and 16and, as illustrated, two bone screws 25 attached to the anchor portion8. A closure structure 32 is used to attach each screw 25 to theassembly 1 with the sleeves 12 and 16 and the anchor portion 8 eachbeing cradled between a lower pressure insert 29 and an upper pressureinsert 30.

With particular reference to FIGS. 2, 32-33, a desired placement of theassembly 1 is shown wherein an arrow C indicates movement of the bonescrews 25 attached to the sleeves 12 and 15 generally in a cephalad orcranial direction. Specifically, FIG. 2 illustrated a pre-compressedassembly 1 in a neutral position, FIG. 32 illustrates compression of thespacers 10,14 and FIG. 33 shows extension or tension of the assembly atspacers 10,14 and movement of the sleeves 12 and 16 in a cephaladdirection (arrow c). FIGS. 32-33 illustrate how the assembly 1 allowsgreater movement of the sleeves and thus the bone screws 25 and attachedspinal segments in the cephalad direction than in the caudad direction,the elastic bumper 18 being the most compressible component of theassembly 1 and the spacer 14 being more elastic and thus morecompressible than the spacer 10 due to the geometry thereof (e.g., anextra groove in the spacer 14). In other embodiments of the invention,the spacer 14 may be made from a material of different durometer thanthe spacer 10, to allow for a desirable increased upward or cephaladmovement of a portion of the assembly 10.

With reference to FIGS. 34 and 35, supported spinal extension as well asmovement in the cephalad direction C is also possible with the assembly1. The washers 11, 13 and 15 are slidable and rotatable with respect tothe cooperating sleeves 12 and 16, advantageously providing steady,balanced and controlled load distribution during angulation, both spinalextension and flexion as well as during compression and tension.Furthermore, the washers 11, 13, and 15 and sleeves 12 and 16 cooperatewith the spacers 10 and 14 to aid in bending and tilting of the assembly1, supporting and controlling the spine in response to lordosis andkyphosis, for example, and also providing for rotation and tilting ofthe assembly in both coronal and sagittal planes, supporting andcontrolling the spine in the case of scoliosis as shown in FIGS. 36 and37. Thus, once attached to the bone screws 25, the assembly 1 issubstantially dynamically loaded and oriented relative to thecooperating vertebra, providing relief (e.g., shock absorption) andprotected movement with respect to not pnly flexion and extension, butalso to distractive, compressive, torsional and shear forces placed onassembly 1 and bone screws 25.

If removal of the assembly 1 from any of the bone screw assemblies 25 isnecessary, or if it is desired to release the assembly 1 at a particularlocation, disassembly is accomplished by using a driving tool (notshown) with a driving formation cooperating with the closure structure32 to rotate and remove the closure structure from the receiver 28.Disassembly is then accomplished in reverse order to the proceduredescribed previously herein for assembly.

Eventually, if the spine requires more rigid support, the connectingmember assembly 1 according to the invention may be removed and replacedwith another longitudinal connecting member, such as a solid rod, havingthe same diameter as the rod portions 8, utilizing the same bone screw25 components. Alternatively, if less support is eventually required, aless rigid, more flexible assembly, for example, an assembly 1 made withelastic spacers and bumper of different durometer or geometry mayreplace the assembly 1, also utilizing the same bone screws 25.

With reference to FIGS. 38-44, an alternative embodiment of a dynamiclongitudinal connecting member, generally 201 is substantially similarto the assembly 1 with the exception that it is shorter than theassembly 1, cooperating with fewer bone screws along an elastic and moreflexible portion thereof. Similar to the assembly 1, the assembly 201provides for greater movement in the cephalad direction as indicated bythe arrow marked CC. The assembly 201 includes an anchor member,generally 204, having an elongate segment or inner core 206 and a boneanchor attachment portion 208; an elastic spacer 210; a pressure washer211; a sleeve 216; an elastic bumper 218; and a crimping ring 220; allsubstantially symmetrically aligned with respect to a central axis AA ofthe anchor member 204. The elongate core 206 of the anchor member 204 isreceivable within the spacer 210, the washer 211, the sleeve 216, thebumper 218 and the crimping ring 220. Thus, the axis AA of the anchormember 204 is also the axis of the fully assembled assembly 201. Whenfully assembled and fixed with all components fixed in position, thespacer 210 and the bumper 218 are placed in compression as shown in FIG.40 and an elastic over-mold or covering 222 is applied about a buttressplate 240 of the anchor 204, the spacer 210, the washer 211 and aportion of the sleeve 212 (the covering 222 shown in phantom in FIG. 40)prior to attachment to three bone screws 25 as shown in FIG. 38.

In the illustrated embodiment, the anchor member 204 is substantiallysimilar to the anchor member 4 previously described herein with respectto the assembly 1. Therefore, the member 204 includes the core 206, thebone anchor attachment portion 208 and the integral buttress plate 240identical or substantially similar in size and shape to the respectivecore 6, attachment portion 8 and buttress plate 40 of the anchor member4 previously described herein. The member 204 differs from the member 4only in that the length of the core 206 is shorter than the core 6 asthe core 206 holds only one sleeve 216, one cooperating spacer 210 andone washer 211 as compared to the core 6 that holds two sleeves, twospacers and three cooperating washers. The spacer 210 is identical orsubstantially similar to the spacer 10 previously described herein. Thesleeve 216 is identical or substantially similar to the sleeve 16,having a concave end surface 274 identical or substantially similar tothe concave end surface 74 of the sleeve 16 previously described herein.The washer 211 is identical or substantially similar to the washer 11previously described herein, having a substantially convex end surface304 identical or substantially similar to the end surface 104 os thewasher 11. The surface 304 is slidably engageable with the concavesurface 274 of the sleeve 216 such that a full and even surface contactoccurs between the sleeve 216 and the washer 211, providing better loaddistribution along the assembly 201, keeping stresses on the inside ofthe sleeve 216 rather than on an outer surface during angulation,translation and compression. The bumper 218 and the crimping ring 220are identical or substantially similar to the respective bumper 18 andthe crimping ring 20 previously described herein with respect to theassembly 1.

The assembly 201 is assembled in a manner substantially similar to themanner of assembly previously described herein with respect to theassembly 1, the assembly 201 however, does not include a second spaceror second sleeve. Therefore, the core 206 is first received within athrough bore of the spacer 210, followed by the washer 211, then withinan inner surface of the sleeve 216, followed by an inner through bore ofthe bumper 218 and then an inner through bore of the crimping ring 220.Similar to what has been described previously with respect to theassembly 1, the core 206 may initially be of a longer length measuredalong the axis AA than is shown in the drawing figures, allowing for amanipulation tool to grasp the core 206 near an end thereof that extendsthrough the crimping ring bore. The spacer 210 and bumper 220 arecompressed, followed by deformation of the crimping ring 220 against thecore 206. Then, the covering 222 is fabricated about the plate 240, thespacer 210, the washer 211 and an end portion of the sleeve 216. Theassembly is now in dynamic relationship with the spacer 210, washer 211,sleeve 216 and bumper 218 being slidable with respect to the core 206,the sleeve 216 being more readily movable in a direction toward thebumper 218 due to the greater elasticity of the bumper 218 as comparedto the spacer 210.

The assembly 201 may then be implanted, cooperating with three bonescrews 25 as illustrated in FIG. 38 and as previously described hereinwith respect to the assembly 1. Unlike the assembly 1 that provides fora more dynamic and flexible connection between three illustrated bonescrews 25, the assembly 201 provides for dynamic stabilization betweenfirst and second bone screws 25 and a more rigid connection between thesecond bone screw 25 and a third bone screw 25 as both the second andthird bone screws are attached to the rigid attachment portion 208.

FIGS. 41 and 42 illustrate a range of axial or spinal movement of theassembly in a cephalad direction as noted by the arrow CC. FIG. 41 showsthe spacer 210 being compressed and thus the sleeve 216 and attachedbone screw 25 moving in a caudal direction. FIG. 42 shows the bumper 218in a fully compressed state with the sleeve 216 and attached bone screw25 moving in a cephalad direction. As illustrated in FIG. 42, theoptional over-mold 222 covers the portion of the assembly 201 that isbeing stretched and tensioned, covering a gap formed between the sleeve216 and the pressure washer 211, protecting spinal tissue and retainingany wear debris within the assembly 201.

With reference to FIG. 43, the assembly 201 is shown in an angulated orbent position as it would be in response to spinal extension, forexample. The load on the assembly 201 being stabilized by movement ofthe pressure washer 211 with respect to the sleeve 216 and also bypartial compression of the spacer 210 along a groove thereof.

With reference to FIG. 44, the assembly 201 is shown in an angulated orbent position as it would be in response to spinal flexion, for example.The load on the assembly 201 is also distractive, causing a gap betweenthe sleeve 216 and the pressure washer 211. The over-mold 222advantageously stretches and prevents tissue from entering into the gapbetween the sleeve 216 and the washer 211.

With reference to FIGS. 45-47, an alternative embodiment of a dynamiclongitudinal connecting member, generally 301 is substantially similarto the assembly 1 with the exception of some aspects of the geometry ofthe sleeve or tube trolley members, one of the spacers and two of thepressure washers located on either side of such spacer. Similar to theassembly 1, the assembly 301 provides for greater movement in thecephalad direction as indicated by the arrow marked CCC. The assembly301 includes an anchor member, generally 304, having an elongate segmentor inner core 306 and a bone anchor attachment portion 308; elasticspacers 310 and 314; pressure washers 311, 313 and 314; sleeves or tubetrolleys 312 and 316; an elastic bumper 318; and a crimping ring 320,all substantially symmetrically aligned with respect to a central axisAAA of the anchor member 304. The elongate core 306 of the anchor member304 is receivable within the spacers 310 and 314, the washers 311, 313and 315, the sleeves 312 and 316, the bumper 318 and the crimping ring320. Thus, the axis AAA of the anchor member 304 is also the axis of thefully assembled assembly 301. When fully assembled and fixed with allcomponents fixed in position, the spacers 310 and 314 and the bumper 318are placed in compression as shown in FIG. 45 and an optional elasticover-mold or covering 322 is applied about a buttress plate 340 of theanchor 304, the spacer 310, the washer 311 and a portion of the sleeve312 and an optional elastic over-mold or covering 323 is applied about aportion of the sleeve 312, the washer 313, the spacer 314, the washer315 and a portion of the sleeve 316, both over-molds 322 and 323 moldedover such component parts prior to attachment of the assembly 310 tothree bone anchors such as the bone screws 25, in the same positionsshown for the assembly 1 in FIG. 32, for example.

The anchor member 304, the spacer 310, the pressure washer 311, thesleeve 312, the bumper 318 and the crimping ring 320 are identical orsubstantially similar to the respective anchor member 4, spacer 10,pressure washer 11, sleeve 12, bumper 18 and crimping ring 20 of theassembly 1 and therefore shall not be discussed in great detail herein.The sleeve 312 has a curved inner surface 354 substantially similar tothe curved inner surface 54 previously described herein with respect tothe sleeve 12. The sleeve 316 has a curved inner surface 355 that isalso substantially similar to the curved inner surface 54 previouslydescribed herein with respect to the sleeve 12. In substantially allother aspects of form and function, the sleeve 316 is substantiallysimilar to the sleeve 16 previously described herein with respect to theassembly 1. The sleeve 312 includes a pair of opposed end plates 358 and360 and the sleeve 316 includes a pair of opposed end plates 362 and363. The illustrated plates 358, 360, 362 and 363 have outer cylindricalsurfaces 364, 366, 368 and 369, respectively, that are substantiallysmaller in diameter than an outer diameter of the spacer 314 and thewashers 313 and 315, allowing gaps for greater relative tilting orarticulation of the sleeves 312 and 316 with respective adjacent washers313 and 315, as will be described in greater detail below.

Thus, the assembly 301 primarily differs from the assembly 1 in thegeometry of the washers 313 and 315 and the spacer 314. The elasticspacer 314 is substantially similar to the spacer 14 in form, functionand materials with the exception that rather than having opposed planarside surfaces 90 and 91, the spacer 314 has opposed side surfaces 390and 391 that are curved and concave. In particular, the illustratedsurfaces 390 and 391 are cupped shaped, sized and shaped to closelyslidingly mate with the dome shaped washers 313 and 315, as will bedescribed in greater detail below, allowing for articulating movementbetween the spacer 314 and the washers 313 and 315, in addition tocompression of the spacer 314.

The pressure washers 313 and 315 are identical to one another and alsoare substantially similar to the pressure washer 11 previously describedabove with the exception that the washers 313 and 315 have opposed,curved, convex side surfaces sized and shaped for cooperation with asubstantially concave surface of a cooperating sleeve 312 or the concavesurfaces 390 or 391 of the spacer 314. The illustrated washer 313 hasopposed curved surfaces 402 and 404 and the washer 315 has opposedcurved surfaces 402′ and 404′.

The assembly 301 is assembled in a manner substantially similar to themanner of assembly previously described herein with respect to theassembly 1. Also, similar to what has been described previously withrespect to the assembly 1, the core 306 may initially be of a longerlength measured along the axis AAA than is shown in the drawing figures,allowing for a manipulation tool to grasp the core 306 near an endthereof that extends through the crimping ring bore. The spacers 310 and314 and the bumper 318 are compressed, followed by deformation of thecrimping ring 320 against the core 306. Then, the coverings 322 and 323are fabricated on the assembly 301 at the locations shown in the figuresand as described above. The assembly 301 is now in dynamic relationshipwith the spacers 310 and 314, washers 311, 313 and 315, sleeves 312 and316 and bumper 318 being slidable with respect to the core 306, bothsleeves 312 and 316 being more readily movable in a direction toward thebumper 318 due to the greater elasticity of the bumper 318 as comparedto the spacers 310 and 314.

The assembly 301 may then be implanted, cooperating with three bonescrews 25 as previously illustrated with respect to the assembly 1. Likethe assembly 1, the assembly 301 provides for a dynamic and flexibleconnection between three bone anchors. Furthermore, the double domedarticulating wear washers 313 and 315 cooperating with the cupped spacer314 allow for increased flexion and extension over the assembly 1 havingthe spacer 14 with planar surfaces. While the assembly 1 spacer 14, forexample, elastically compresses when the assembly bends during spinalflexion or extension, the pressure washers 313 and 315 may slidinglyarticulate along the surfaces 390 and 391 of the spacer 314 duringspinal flexion or extension. If compression accompanies the bendingmovement, the spacer 314 may also compress slightly in response to thespinal movement. As illustrated in FIG. 47, the end plates 358 and 360of the sleeve 312 and the end plates 362 and 363 of the sleeve 316 aresized and shaped to have a smaller outer diameter than the pressurewashers and spacers of the assembly 301 as well as provide a gap betweensuch plates and adjacent components of the assembly 301, providingclearance for articulated movement between the components.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

What is claimed and desired to be secured by Letters Patent is asfollows:
 1. A longitudinal connecting member adapted for cooperationwith a plurality of bone anchors implanted in a spine, the improvementwherein the longitudinal connecting member comprises: a) a substantiallyrigid anchor portion extending along a longitudinal axis of theconnecting member, the anchor portion being formed of a first materialand being directly engaged by first and second bone anchors; b) a coreportion joined with an end of the anchor portion, extending along thelongitudinal axis and indirectly engaged by a third bone anchor, thecore portion being formed of a second material and having a reduceddiameter relative to the anchor portion, wherein the second material andthe reduced diameter cooperate so as to enable at least some flexing ofthe core portion; c) a first inelastic sleeve slidingly received overthe core portion so as to be located between the third bone anchor andthe core portion; c) a pair of elastic spacers received over the coreportion such that each of the spacers is adjacent to an end of the firstsleeve; d) a crimp ring engaging the core portion and being located soas to bias the spacers; and e) an elastic over-mold surrounding the atleast one of the spacers and a respective adjacent end of the firstsleeve; wherein f) the longitudinal connection member provides forgreater movement in the cephalad direction than in the caudad direction.2. The improvement of claim 1, wherein a) the elastic over-mold gripsboth the anchor portion and the first sleeve.
 3. The improvement ofclaim 1, wherein a) the anchor portion includes has a first end plateand the elastic over-mold is molded about the first end plate.
 4. Theimprovement of claim 1, wherein a) the elastic over-mold is made from acomposite material comprising elongate reinforcement strands imbedded ina polymer.
 5. The improvement of claim 1, wherein a) the core is madefrom a polymer.
 6. The improvement of claim 5, wherein a) the polymer ispolyetheretherketone.
 7. The improvement of claim 1, wherein a) thefirst sleeve substantially blocks flexing of the portion of the corethat is surrounded by the first sleeve.
 8. The improvement of claim 7,wherein a) the core flexes primarily between the first sleeve and theanchor portion.
 9. The improvement of claim 1, wherein the longitudinalconnecting member further comprises: a) a second inelastic sleeveslidingly received over the core portion so as to be located between afourth bone anchor and the core portion; b) a third elastic spacerreceived over the core portion so as to be located between the secondinelastic sleeve and the crip ring; and c) a second elastic over-moldsurrounding a second end of the first sleeve, the third spacer and anadjacent end of the second sleeve.
 10. The improvement of claim 9,wherein: a) the first sleeve substantially blocks flexing of the portionof the core that is surrounded by the first sleeve; and b) the secondsleeve substantially blocks flexing of the portion of the core that issurrounded by the second sleeve.
 11. The improvement of claim 10,wherein a) the core flexes primarily: i) between the first sleeve andthe anchor portion; and ii) between the first sleeve and the secondsleeve.